The present invention generally relates to variable transmission windows. More specifically, the present invention relates to control systems for controlling the transmission of variable transmission windows and to various constructions of variable transmission windows.
Variable transmittance light filters, such as electrochromic light filters, have been proposed for use in architectural windows, skylights, and in windows and sunroofs for automobiles. Such variable transmittance light filters reduce the transmittance of direct or reflected sunlight during daytime through the window, while not reducing such transmittance during nighttime. Not only do such light filters reduce bothersome glare and ambient brightness, but they also reduce fading and generated heat caused by the transmission of sunlight through the window.
Variable transmission windows have not been widely accepted commercially for several reasons. First, they tend to be very expensive due to the cost of materials required for their construction, and their complex construction makes mass-production difficult. Additionally, electrochromic windows tend to have a lower life expectancy than conventional windows due to degradation of the electrochromic materials used in the windows. The combination of added cost and lower life expectancy has deterred many architects and builders from using electrochromic windows.
Recent advances have resulted in electrochromic windows that cost less and have higher life expectancies. Examples of such electrochromic windows are disclosed in commonly assigned U.S. Pat. No. 6,407,847, entitled “ELECTROCHROMIC WINDOWS AND METHOD OF MANUFACTURING THE SAME.” Perhaps because electrochromic windows had not previously been widely accepted commercially, little thought had been given to practical window constructions that enable power to be delivered to an electrochromic window element through conventional types of window frame assemblies. While electrochromic windows have been discussed in the prior art, the typical construction that is disclosed merely shows two or more wires extending from a window frame in which the electrochromic window elements are mounted. Such a construction does not allow for electrochromic window elements to be mounted in a window sash that moves relative to a stationary window frame, nor do such constructions allow for easy construction of such window assemblies or easy replacement of an electrochromic window element. In general, electrochromic window assemblies can be relatively heavy, as may conventional window assemblies. Thus, if the window installers must additionally handle dangling wires from a window assembly when attempting to install the window assembly in a building, an additional person may be required just to manage the wires as the windows are being installed. Further, once the wires are secured to a power source, replacement of the windows is more difficult.
The prior art also fails to address techniques for controlling the transmission of a plurality of such electrochromic windows in a building either independently or in various groupings. Therefore, there exists a need for an electrical control system for controlling the transmittance of a plurality of variable transmission windows in a building.